The OTN is a transport network which is on the basis of the wavelength division multiplexing technology and in the optical layer organization network, and is the next generation backbone transport network. For the OTN, since the rate of the transmitted signals is higher, the amount of carried information is larger, and the wavelength/sub-wavelength service scheduling capability is provided, thus network protection of the OTN becomes more important for traditional network protection, and the protection capability is also stronger.
In the OTN, an ODUk (Optical Data Unit k) layer generally is required to provide end to end sub-network link protection. At present, protection methods commonly used in the industry include 1+1 protection, 1:n protection and channel shared protection, etc. In selecting a protection scheme, a choice is often required to be made based on bandwidth utilization ratio, protection robustness and switching time.
The 1+1 protection may provide a dedicated backup channel for each sub-network link, and same signals are transmitted in a working channel and a protection channel. Thus such protection method has the strongest robustness and the shortest switching time. However, the bandwidth utilization ratio is only 50%, and the bandwidth is wasted severely in the case of very low network alarm ratio.
The channel shared protection is a protection method where all services share backup resources and is applied in the ring network, thus its bandwidth utilization ratio is much higher than that of the 1+1 protection method. Its robustness is also higher than that of the 1:n protection, since working resources and protection resources are separated. However, when the nodes in the ring gradually increase, its stability is decreased thereupon too. Especially when alarms occur at multiple ODUks, a phenomenon of service misconnection will occur; even if misconnection does not occur, for the alarms occurring at multiple ODUks, the channel shared backup resources can only provide one service for switching such that a plurality of services with failures can not be protected simultaneously. FIG. 1 is a schematic diagram of a case where service protection is performed using a channel shared protection way when a single ODUk alarm occurs in the ring network. It can be seen from the figure that services will be triggered to switch at two ends when an alarm of an Optical Channel (OCH) layer is detected, and services that are also clockwise (anticlockwise) share the same inverse anticlockwise (clockwise) ring channel. FIG. 2 is a schematic diagram of a case where a channel shared protection way cannot be used to perform service protection when multiple ODUk alarms occur in the ring network. It can be seen from the figure that if two or more ODUk alarms are detected in a direction, for example, in a clockwise ring, the channel shared protection is unable to switch more than two services to the shared protection channel, resulting in protection failure.